I am wondering if anyone know what the allowable tire diameter differance is. I have 275/40/17 (25.66 in) on mine and am wanting to use a either a C5/4 spare with a 25.54 (C4) or 24.99 (New GTO). Any help would be appreciated.

I would get as close as possible, .12 is pretty good and only .3768 " per rotation and only for an emergency right ?